Big Bear Lake, Calif.

Wally Skalij/Los Angeles Times

San Bernardino County sheriff's deputies battle the cold Friday during the hunt for murder suspect Christopher Dorner. In frigid conditions, life-threatening hypothermia can strike in less than an hour.

San Bernardino County sheriff's deputies battle the cold Friday during the hunt for murder suspect Christopher Dorner. In frigid conditions, life-threatening hypothermia can strike in less than an hour.